1. Field of the Invention
The present invention relates to a multiple-input single-output circuit and a display device, and more particularly to a circuit in which one output voltage is determined based on voltages input from a plurality of input terminals and a display device using the circuit.
2. Background Art
Display devices have been widely used as information communication terminals such as computers or the displaying devices of television receivers. In liquid crystal display devices represented by the display devices, the alignment of liquid crystal molecules sealed between two substrates is changed to change the degree of light transmission, whereby an image to be displayed is controlled. In a driver circuit that drives the display device, a decoder circuit for outputting a voltage corresponding to a gray-scale value for each pixel is mounted. The decoder circuit has been increasing in scale along with an increase in gray-scale level in recent years, which increases an area of the decoder circuit occupying a chip. Therefore, the decoder circuit is required to be miniaturized.
JP-A-2001-34234 discloses a technique of reducing the number of wires for gray-scale and the scale of a decoder by using a two-input amplifier that outputs, when two input voltages are the same, the input voltage and outputs, when they are different from each other, an intermediate voltage between the two voltages.
In the technique, however, it is pointed out that when the difference between the two different, input voltages is large, a voltage to be output is shifted to the high-voltage side. For eliminating the shift to the high-voltage side, JP-A-2006-310958 and JP-A-2005-130332 propose a technique of outputting an intermediate voltage by using two constant current sources and a current mirror circuit.
However, for configuring a circuit having two constant current sources with the same current, a half of the current has to flow into each of the constant current sources. Therefore, it is necessary to make a gate width narrower or a gate length longer. Making the gate length longer leads to an increase in the area of the circuit occupying a chip. On the other hand, making the gate width narrower leads to the difficulty in the process, which might cause deterioration in yield.